ROOT HABITS OF DESERT PLANTS. 3^ 



culty in removing the root-system and keeping it intact. However, great 

 care was always taken to obtain as much of the roots as possible. A shoot 

 of a mature plant of Amsinckia 13.5 cm. in length had a tap root over 8 cm. 

 long; a plant with a shoot 18 cm. long had a tap root more than 12.5 cm. 

 in length. Thus, although the greatest penetration was not learned, it w^as 

 sufficient to enable the plant to reach and to tap a relatively good water 

 supply at a time when the upper layers of the soil were too dry to provide 

 a sufficient amount of water for plants whose roots were entirely restricted 

 to the surface soil layers (plate 5). 



Astragalus Nuttallianus. 



In this vicinity Astragalus grows under a large variety of conditions as 

 regards exposure, kinds of soil, and relations to other plants. It is practi- 

 cally cosmopolitan in its local distribution. A mature plant with a shoot 

 6 cm. long, together with young specimens, was preserved for examination. 

 The leading character of its root-system was the well-developed tap root, 

 13 cm. in length. The laterals were few and coarse, and little branched. 

 Tubercles were present in considerable abundance. 



BowLESiA Lobata. 



Boivlesia is to be found on Tumamoc Hill and on the lower detrital slopes, 

 and usually occurs under the protection of a shrub or tree or in other situ- 

 ations where the water relations are relatively favorable. The leaves are 

 large and the plant has the appearance of being ill-adapted to successfully 

 withstand very severe arid conditions. The root-system is not an extensive 

 one, and is characterized byhavingamain root and lateralsof the first order 

 of about the same diameter and by the relative coarseness of all the roots. 

 The main root does not go straight down, but zigzags downward in a very 

 irregular fashion. From the main root there arise, at intervals of about a 

 centimeter, rather coarse laterals which branch sparsely. It seems prob- 

 able, although not proved by actual experiments, that the restricted dis- 

 tribution of Boivlesia may be directly associated with the shallowly placed 

 and poorly developed root-system of the plant. 



Brodi^a Capitata. 



Brodicea is restricted in its distribution to Tumamoc Hill and to the upper 

 bajada slope, and does not occur in the other habitats, namely, Santa Cruz 

 flood-plain or that by West Wash, or on the bajada as a whole. It is a 

 bulbous perennial with the vegetative and flowering periods in the winter 

 season. Its bulbs are somewhat over i cm. in diameter, and are 5 cm., 

 more or less, beneath the surface of the ground . The roots are adventitious, 

 coarse, and unbranched. They are relatively few and are usually more 

 than 5 cm. in length. The depth to which the roots of the plant penetrate, 

 therefore, is approximately 10 cm. 



